In order to drive a switching element used in an inverter or the like, a drive circuit which drives the switching element on the basis of an on/off signal input from an external control system is used.
In general, in order to prevent an excessive current from flowing through a switching element due to an accident such as short of load circuit and destroying the switching element, means which cut off the switching element to protect the switching element and a load circuit when an overcurrent has occurred is provided in the drive circuit. If the switching element is cut off according to an ordinary method when an overcurrent has occurred, however, large di/dt is generated and a surge voltage of Ldi/dt occurs due to inductance L of wiring or the like. The surge voltage exceeds the withstand voltage of the switching element and the element is destroyed, in some cases. Therefore, a function of preventing an element from being destroyed by a surge voltage based on large di/dt when an overcurrent has been generated by, for example, short of load circuit is desired.
Furthermore, at the time of off operation for turning off the switching element and in the off-state of the switching element, there is a fear that a gate voltage will be raised by charge stored on collector-gate capacitance of the switching element (IGBT etc.) and the switching element will falsely turn on. Therefore, the drive circuit is demanded to have a function of preventing such false turning on as well.
If a change of the gate voltage of the switching element is large when turning off the switching element, a problem of switching noise occurs. In order to reduce the problem of such switching noise, the drive circuit is demanded to have a function of gradually lowering the gate voltage at the time of switching off.
It is desired to provide the drive circuit simultaneously with the function of preventing the switching element from being destroyed by the surge voltage, the function of preventing the switching element from being falsely turned off, and the function of reducing the problem of the switching noise. If the drive circuit is provided with all of these functions, however, a problem of an increased chip size and an increased cost is caused.